1661809 has 4 divisors (see below), whose sum is σ = 1664740. Its totient is φ = 1658880.

The previous prime is 1661789. The next prime is 1661813. The reversal of 1661809 is 9081661.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 846400 + 815409 = 920^2 + 903^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1661809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661839) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 312 + ... + 1849.

It is an arithmetic number, because the mean of its divisors is an integer number (416185).

2^1661809 is an apocalyptic number.

It is an amenable number.

1661809 is a deficient number, since it is larger than the sum of its proper divisors (2931).

1661809 is an equidigital number, since it uses as much as digits as its factorization.

1661809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2930.

The product of its (nonzero) digits is 2592, while the sum is 31.

The square root of 1661809 is about 1289.1117096668. Note that the first 3 decimals coincide. The cubic root of 1661809 is about 118.4478100455.

The spelling of 1661809 in words is "one million, six hundred sixty-one thousand, eight hundred nine".